1. Field of the Invention
Embodiments of the invention generally relate to a gas distribution plate assembly and method for distributing gas in a processing chamber.
2. Description of the Background Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent glass substrate (for flat panel) or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture into a vacuum chamber that contains a flat panel. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material on a surface of the flat panel that is positioned on a temperature controlled substrate support. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
Flat panels processed by PECVD techniques are typically large, often exceeding 370 mm×470 mm and ranging over 1 square meter in size. Large area substrates approaching and exceeding 4 square meters are envisioned in the near future. Gas distribution plates utilized to provide uniform process gas flow over flat panels are relatively large in size, particularly as compared to gas distribution plates utilized for 200 mm and 300 mm semiconductor wafer processing.
Large gas distribution plates utilized for flat panel processing have a number of fabricating issues that result in high manufacturing costs. For example, gas flow holes formed through the gas distribution plate are small in diameter relative to thickness of the gas distribution plate, for example a 0.016 inch diameter hole through a 1.2 inch thick plate, resulting in a high frequency of drill bit breakage during hole formation. Removal of broken drill bits is time consuming and may result in the entire gas distribution plate being scrapped. Additionally, as the number of gas flow holes formed through the gas distribution plate is proportional to the size of the flat panel, the great number of holes formed in each plate disadvantageously contributes to a high probability of trouble during plate fabrication. Moreover, the high number of holes coupled with the care required to minimize drill bit breakage results in long fabrication times, thereby elevating fabrication costs.
As the cost of materials for manufacturing the gas distribution plate is great, it would be advantageous to develop a gas distribution plate in a configuration that can be efficiently and cost effectively fabricated. Moreover, as the size of the next generation gas distribution plates is increased to accommodate processing flat panels in excess of 1.2 square meters, resolution of the aforementioned problems becomes increasingly important. While addressing the cost implications of the design of large gas distribution plates is important, performance attributes must not be overlooked. For example, the configuration, location and density of gas flow holes directly impact deposition performance, such as deposition rate and uniformity, and cleaning attributes, such as cleaning efficiency and residual cleaning chemical(s) in the process chamber.
Therefore, there is a need for an improved gas distribution plate assembly that reduces the manufacturing cost, and has good deposition and cleaning performance.